This invention relates to a chemical processing system for processing substrates such as silicon wafers in the manufacture of electronic devices such as integrated circuit chips.
In the processing of substrates or wafers in the manufacture of electronic devices such as integrated circuit chips, a chemical processing system is used which requires the application, in sequence, of a number of different chemicals to the substrate of being processed. Some of the chemicals are applied alone, and others are mixed together. Such acids as hydrochloric acid, sulfuric acid, nitric acid and hydrogen fluoride are applied to the wafers in processing steps, and may in some steps be mixed with such others chemicals as hydrogen peroxide.
Nitrogen gas under pressure is also applied at the liquid nozzles in order to atomize the liquid chemicals as they are directed into the processing chamber and toward the substrates in order to thoroughly drench the wafers and assure that full coverage by the liquid chemical is obtained. Water is also used as a rinsing agent to clean the substrates between the process steps and to purge the chemical lines or ducts of liquid chemicals.
In processing of such substrates, the substrates may be held stationary, or may be revolved, and in some instances processing of wafers is done one at a time, and in other instances batches of wafers are processed simultaneously in a processing chamber. Also, the spray parts which direct the spray of chemical and water into the processing chamber may be located at the peripheral wall of the chamber, but the spray posts may also be located approximately at the center of the chamber and directing sprays outwardly, in a general radial direction therefrom, as to apply the sprays of liquids and water to the wafers in the chamber.
It is essential that the chemical delivery lines which supply chemicals to the spray post be rinsed out between successive chemical steps in the process, in order to prevent chemical reactions leading to precipitates and other detrimental by-products, which might be produced if chemicals used in successive steps were allowed to mix with each other. For these same reasons, it is also essential to assure that the chemicals applied to the substrates in each step are thoroughly rinsed off prior to applying chemicals in subsequent steps.
In the past, it has been conventional to supply liquid chemicals, and nitrogen gas into a spray post for directing the liquid spray into the processing chamber and simultaneously, with the nitrogen under pressure, to break up the spray particles and effectively atomize the liquid spray in the chamber in order to throughly drench the substrate during the chemical step.
When the chemical step has been completed, it has been conventional practice to terminate the flow of the liquid chemical into the chemical lines, and simultaneously direct water into the chemical lines under pressure so as to gradually purge liquid chemicals from the supply lines and from the nozzle orifices; and while this purging has continued, the concentration of liquid chemicals being applied to the substrates in the processing chamber is gradually diminished. Simultaneously with the application of rinsing water to the chemical lines, rinsing water is also applied from a separate nozzle or series of nozzles which emanate a fan shaped spray of rinsing water into the processing chamber. This fan shaped spray of rinsing water has not been atomized and is therefore not adequate for throughly rinsing the wafers, but the rinsing of the wafers depends on the atomized spray from the chemical spray post, now emanating atomized water. It has been recognized that the rinsing of the chemical delivery lines must be first accomplished and subsequently the rinsing of the substrates with atomized water from the chemical supply post is then subsequently accomplished. This two step rinsing, first of the chemical delivery lines and then of the substrates has taken an excessive length of time to essentially slow down the overall processing of the substrates; and the previous rinsing procedure also has the disadvantage of not defining a specific termination of application of the chemical to the substrates in that the chemical is continuing to be applied to the substrates until the purging water has diluted the chemicals in the lines so that no more such chemical exists.